Known tool changeover holders have a rotating spindle that has on the machine-tool end a central journal with a chuck and an annular face surface. A tool head is arranged so as to be replaceable on the spindle, and on the spindle side incorporates a central bore to accommodate the spindle journal and tighten it axially by means of a chucking device. The bore is surrounded concentrically by an annular matching surface.
The face and matching surface are provided with congruent centering and torque-transmitting means that engage each other in the chucked position. In this connection, a distinction must be drawn between two systems that differ in principle: In the first system, concentric, annular contact surfaces are provided on the face or matching surface of the spindle or tool head. The centering between these two components is effected by the engagement of the spindle journal into the tool-head bore. The transmission of torque is effected by a coupler block in the area of the face surface of the journal which, when in the chucked position of the tool head on the spindle, fits into a corresponding force-fit recess in the matching surface of the tool head. The second known alternative is to provide so called Hirth serrations in the area of the face and matching surfaces of the spindle and the tool head. These rows of radial serrations or teeth, which are arranged on annular rings in each instance concentric with the axis of the spindle, offer certain advantages relative to the flat contact surfaces with regard to the accuracy with which the tool head can be centered on the spindle and the transmission of torque. However, the production of changeover tool holders with such serrations entails much higher production costs than changeover tool holders with flat contact surfaces.
The changeover tool holders for machine tools and in particular for the so-called processing centers operate with tool heads that hold tools of various kinds, depending on the particular application. Varying demands on centering precision and torque transmission between tool head and spindle are imposed, depending on the processing stage and the associated permissible tolerances. Thus, a tool changeover holder with flat contact surfaces could be perfectly adequate for one particular processing stage, whereas serrations would be of advantage for another. However, because of the configuration of the particular spindle face with either a flat contact surface or serrations, there is no possibility of interchanging one for the other.
It is therefore an object of the present invention to provide a tool changeover holder, the spindle of which permits the use of a tool head with either a flat contact surface or one with Hirth serrations.